Rock heater for sauna bath

ABSTRACT

AN IMPROVED ROCK HEATER WHEREIN AN IMPERFORATE ROCK BOX EXTENDS INTO AND CLOSES THE TOP OF A GENERALLY CONTINUOUS SIDE WALL ENCLOSING A COMBUSTION REGION. AIR FOR SUPPORTING COMBUSTION IN THE REGION IS PREHEATED AS IT FLOWS TOWARD THE SAME ALONG A PASSAGE BETWEEN THE WALL AND A CASING SURROUNDING THE WALL. EXHAUST GASES ARE DIRECTED ALONG AN INCLINED PATH FROM AN AREA SURROUNDING THE OUTER SURFACE OF THE ROCK BOX AND INTO THE ATMOSPHERE. IN ONE FORM. THE ROCK HEATER HAS THE EXHAUST PATH EXTENDING THROUGH THE ROCK BOX AND IN ANOTHER FORM, THE ROCK BOX HAS A CONCICAL SURFACE.

United States Patent Kolkka Feb. 5, 1974 ROCK HEATER FOR SAUNA BATH [76] Inventor: Toivo 1. Kolkka, 2030 Park Emmi"e"Edward Paws Boulevard, Palo Alto. Calif Attorney-Townsend and Townsend [22] Filed: Dec. 8, 1971 [57] ABSTRACT v PP 205,824 An improved rock heater wherein an imperforate rock Related Application Data box extends into and closes the top of a generally con- [63] Continuatiomim an of Ser No 852 838 Au 25 tinuous side wall enclosing a combustion region. Air 1969 abandone: for supporting combustion in the region is preheated I as it flows toward the same along a passage between I [52] US. Cl. 126/344 the wall and a casing Surrounding the wall Exhaust [51] Int. Cl. 24h 3/14 I gases are directed along an inclined path from an area [58] Field of Search 5 263/19 surrounding the outer surface of the rock box and into I. I the atmosphere. In one form, the rock heater has the [56] References Cited exhaust path extending through the rock box and in another form, the rock box has a conical outer sur- UNITED STATES PATENTS face. 3,022,782 2/1962 Bryant 126/344 3,372,264 3/1968 Williams 126/344 20 Claims, 10 ra ing Figures PATENTED 3 789 827 sum 1 BF 3 FIG.|

PAIENTE FEB 5am SHEU 3 OF 3 FIG.9

ROCK HEATER FOR SAUNA BATH This is a continuation-in-part application of application Ser. No. 852,838, filed Aug. 25, 1969, and now abandoned entitled Rock Heater for Sauna Bath.

This application relates to improvements in a rock heater usable in a sauna bath and, more particularly, to a rock heater having means to preheat air used to support combustion in a region below an imperforate rock box.

In utilizing a rock heater in a sauna bath, it is desirable that the heater be as efficient as possible with respect to heat transfer from the heat source thereof to the rocks in the rock box of the heater so that the rocks will be heated in a minimum of time and, if a gas burner is used as the heat source, only a minimum volume of gas need be supplied to the burner itself. Moreover, it is important to prevent air pollution by assuring that non-combustible gases be prevented as far as possible, from passing into the atmosphere.

Conventional rock heaters using gas burners are relatively inefficient because their structural elements are generally arranged such that the air-gas mixture supplied to the burner is not properly conditioned to achieve maximum combustion of gases. Thus, there is always a certain volume of non-combustible gases which do not contribute to the generation of heat for heating the rocks in the rock box and these gases are exhausted to the atmosphere as pollutants.

The present invention provides a rock heater having air preheating means so that the air used to support combustion therein will be properly conditioned to achieve optimum combustion of gases. Thus, the invention provides a means to achieve greater heat content in the gases for a given volume of gas supplied to a gas burner of the rock heater. Heating of rocks in the rock box of the heater of this invention is, therefore, much more efficient than can be achieved with conventional rock heaters and the pollution problem associated with venting some combustible gases to the atmosphere is minimized.

The rock box of the present invention is also configured to achieve maximum heat transfer from the combustion gases so that the rocks in the rock box will be more efficiently heated and maintained at the requisite temperature. One form of the rock box utilizes a polygonal side wall having an exhaust conduit extending therethrough with the outer surface of the rock box closing the top of the chamber in which the heat source is located. Thus, the rocks in the rock box will be heated both by the gases rising from the heat source which contact the outer surface of the rock box and also by gases being passed through the exhaust conduit and out of the rock heater.

Another form of the rock box includes a rock box having a conical wall whose closed apex is at its lower end and which extends partially into the open upper end of a second conical wall defining a part of the enclosure for the heat source and whose apex is at its uppermost end. In this form, the exhaust conduit extends laterally from a region near the apex of each conical wall and the apex of the first conical wall is eccentric to the opening in the second conical wall to assure that a major portion of the combustion gases passing through the opening will contact the outer surface of the first wall before being exhausted through the exhaust conduit. The configurations of the two conical walls are such that the combustion gases follow a spiral path upwardly and about the first wall as they leave the opening in the second wall so that the first wall will be more effectively heated; thus, it can more efficiently impart heat energy to the rocks held therein.

A further aspect of the invention is the placing of the rock heater on one side of a space-dividing wall and drawing in air to the rock heater from the opposite side of the wall. Also, the exhaust gases are exhausted from the rock heater to the opposite side of the wall. In this way, the rock heater does not depend upon air in the.

sauna bath enclosure to support combustion. Also, the exhaust gases will not present a toxic atmosphere in the sauna bath.

The primary object of this invention is to provide an improved rock heater for a sauna wherein the rock heater has means for preheating incoming air to the heat source thereof to provide more efficient combustion of gases used to heat the rocks in the rock box of the rock heater.

Another object of this invention is to provide an improved rock heater of the type described wherein the rock box thereof is constructed to more effectively utilize the gases heated by the heat source thereof to minimize operating costs and to reduce the time required to render the rock heater operable.

The rock heater of this invention is suitable for use with a portable sauna comprised of a number of releasably interconnected walls having tongue and groove structure thereon to permit quick assembly of the walls while providing tight seals at the junctions of the walls.

Thus, a further object of this invention is to provide an improved sauna with which the aforementioned rock heater can be utilized wherein the sauna is comprised of a number of releasably interconnected walls which permit rapid assembly and disassembly yet assure tight seals at the junctions of the walls to minimize heatlose from the sauna during use. Other objects of this invention will become apparent as the following specification progresses, reference being had to the accompanying drawings for an illustration of several embodiments of the rock heater.

IN THE DRAWING:

FIG. 1 is a top plan view, partly broken away and in section, of a first embodiment of the rock heater;

FIG. 2 is a vertical cross-section of a rock heater of FIG. 1;

FIG. 3 is a cross-sectional view taken along lines 3-3 of FIG. 2;

FIG. 4 is a vertical section, similar to FIG. 2, but illustrating a second embodiment of the rock heater; and

FIG. 5 is a horizontal section taken along lines 5-5 of FIG. 4.

FIGS. 6-10 show a portable sauna assembly.

One embodiment of the rock heater of this invention, denoted by the numeral 10, is illustrated in FIGS. 1-3. Heater 10 includes a closed furnace 12 whose polygonal side wall 13 is of heat-conducting material disposed within a casing 14 adapted to be supported on a floor or other suitable surface. Casing 14 need not surround furnace 12 so long as it forms therewith a fluid passage 16. Casing 14 may be made from an insulating material to retain heat therewithin. Furnace 12 is inwardly spaced at least at one side thereof from casing 14 to present fluid passage 16 which communicates with a rectangular conduit 18 secured to and extending laterally from passage 16. Conduit 18 is of sufficient length to extend through wall 20, the latter having a pair of spaced wall sections 22 and 24 and being a wall of a sauna room in which rock heater is disposed. Inner and outer wall seals 25 surround conduit 18. The purpose of conduit 18 is to place passage 16 in fluid communication with the atmosphere exteriorly of wall 20, which is accomplished by opening 26 in the outer end of conduit 18. Opening 26 is located at one side of a rectangular plate 28 having a hole 29 for receiving the open outer end of an extension of a flue pipe 54. Plate 28 is supported by a number of elongated fastener screws 33 coupled in a suitable manner to conduit 18. A deflector plate 31 is disposed below pipe 54 and also serves to support the same.

A flue gas distributer plate 35 is also carried by screws 33 in outwardly spaced relationship to plate 28 and the outer open end of pipe 54. Plate 34 allows flue gases to be moved laterally from the outer open end of the flue pipe regardless of wind conditions. Also, deflector plate 31 allows air to enter conduit 18 regardless of wind conditions.

Passage 16 communicates with a bottom space below furnace 12, where injector tube 32 within space 30 forms part of burner apparatus 34 whose burner 36 is disposed within furnace 12. Gas control device 39 is disposed between fuel gas inlet and pipe 37 at the front of heater 10 (FIG. 1) and controls the gas flow therethrough.

Control 39 also controls the gas flow to a pipe 41 forming a part of a pilot light assembly 38, the latter being located adjacent to burner 36 for use in lighting the burner in the usual manner. A suitable combustible gas, such as natural gas or the like, can be used to operate burner apparatus 34. The gas is directed to injector tube 32 from pipe 35 adapted to be connected to a source of the gas (not shown) and from pipe 37 (FIG. 1) coupled to the front of injector tube 32 (FIG. 2).

Burner apparatus 34 can be modular in construction. Thus, it can be releasably connected to casing 14 and easily inserted in and removed from its operative position, shown in FIG. 2.

The primary air flowing through passage 16 and bottom space 30 passes into injector tube 32 for mixture with the gas as it travels toward burner 36. The air for supporting combustion also flows into a region 42 (FIG. 2) and then through an opening 44 which places region 42 in communication with the combustion region inside furnace 12. Air flowing through opening 44 and into the furnace supports the combustion of gases above burner 36.

The gases of combustion pass upwardly from burner 36 and through a perforated, dome-shaped plate 46 which is immediately below and surrounding the base of a rock-holding box (FIG. 2). The box is imperforate and extends downwardly into the upper end of furnace 12 as well as closes off the open top thereof so that the furnace is effectively closed except for its communication with air passage 16. Also, casing 14 is closed at its top by a top wall 17.

Box 48 is polygonal and has four inclined side walls which present a space 50 surrounding the box into which the hot gases of combustion pass after flowing through holes 52 in plate 46. The box is made up of heat conductive material, such as metallic material, which readily conducts the heat from the gases to the rocks (not shown) in the box so that the rocks will be heated in the manner required for carrying out the purposes of a sauna bath. The upper end of the box is open to receive the rocks.

Flue pipe 54 extends through conduit 18, through side wall 13, and into and through the lower part of box 48 as shown in FIG. 2. One end of flue 54 is open and communicates with space 50 so that the flue can receive the spent flue gases of combustion which are received in the space. The opposite end of flue 54 is also open and communicates with the atmosphere at the outer end of conduit 18. Flue 54 is spaced inwardly from the inner surface of conduit 18 so that incoming air will surround flue 54 and will be preheated thereby.

A mesh cover can be disposed across the open outer end of flue pipe 54 to trap particles of combustion passing therethrough. The flue is inclined to insure removal of the spent flue gases from space 50. Such flue gases pass into the atmosphere exteriorly of wall 20.

In use, rocks to be heated are placed in rock box 48 and, assuming that rock heater 10 is properly located within a sauna room in which sauna baths are to be taken, and the entrance to conduit 18 is on the opposite side of wall 20 from heater l0, burner 36 is lit with the use of pilot light apparatus 38 to generate the gases of combustion for heating the rocks in box 48. Access to the pilot light apparatus 38 can be had through an access door on casing 14.

When burner 36 is lit, the combustion is supported by air drawn into furnace 12 through opening 44. This air comes from the atmosphere exteriorly of wall 20 through opening 26 and through conduit 18, passage 16 and bottom space 30.

The gases of combustion rise in furnace l2 and pass through holes 52 into space 50. The heat of the gases is conducted through box 48 and into the rocks contained therein. By convection, the gases then flow outwardly of space 50, into and through flue 54, and then into the atmosphere exteriorly of wall 20. The section of flue 54 within rock box 48 is also effective to conduct the heat into the rocks disposed in the box. The reason for this is that the spent flue gases may be still hot enough to impart heat energy to the rocks in the box.

As air enters opening 26 and conduit 18 and flows through the latter, the air is first pre-heated by flue 54 which, in turn, is heated by the spent flue gases as they travel toward opening 56 and into the atmosphere. The air passing through passage 16 is also preheated by virtue of its proximity to side wall 13 since the latter is heated by the hot gases of combustion therewithin.

Injector tube 32 of burner apparatus 34 also is heated by conduction from burner 36 so that the air passing through bottom space 30 is preheated by injector tube 32. The preheated primary air entering injector tube 32 and also combustion air passing through opening 44 into furnace 12 provides for a more efficient combustion than is capable with conventional heaters because the heated air is more effectively combined with the gas supplied to the burner. Since the combustion is more efficient, there is a minimum volume of noncombustible gases which pass upwardly through the furnace and into space 50. Thus, greater heat is supplied to heat the rocks in rock box 48. The process of heating the rocks in the box is thus more efficient and economical, since less gas is required to produce a given heating effect.

The bottom of the furnace also imparts heat to the air passing through space 30. Thus, the air is heated in two ways so as to properly elevate the temperature of the air before it is used in the combustion process.

A second embodiment of the rock heater of this invention is illustrated in FIGS. 4 and 5 and is broadly denoted by the numeral 110. Heater 110 includes a furnace 112 having a generally continuous outer side wall 113. A casing 114 at least partially surrounds furnace 1 12 and defines therewith a fluid passage 116, this passage being substantially for the same purpose as passage 16 of the first embodiment of the rock heater. An air entrance conduit 118, shown only partially in FIG. 4, is provided in fluid communication with passage 116 to direct air along a preheating path to the combustion region within furnace 112. Also, the outer end of conduit 118 is substantially the same in construction as that of conduit 18 of the first embodiment. A burner apparatus 134 is located in the bottom of furnace 112 near an air inlet opening 144, whereby air can enter the combustion region and support combustion in the vicinity of burner apparatus 134. A source of gas under pressure is adapted to be coupled with burner apparatus 134 in the same manner as that described above with the first embodiment.

A rock box 136 is disposed in the upper end of furnace 112 and extends partially thereinto as shown in FIG. 4. The rock box is defined by a first conical member 137 having a conical outer surface 138, a closed lowerapex end 140, and an open upper end so that rocks to be heated can be placed in the rock box. The upper, continuous outer periphery 141 is rigidly secured to the inner surface of side wall 113 near its open top to thereby close the latter. Box 136 is formed from any suitable heating conducting material, such as stainless steel, and has an annular, inwardly extending bead 142 surrounding its lower end to provide for expansion and contraction of the material without causing metal fatigue. A cover 143 having a central opening 145 covers the top opening between side wall 113 and casing 114, opening 145 being aligned with the open top of the rock box.

As shown in FIG. 4, apex end 140 of member 137 extends partially into a truncated opening 146 in the upper, apex end of a second conical member 150 whose lower, open end is welded at its outer periphery at several locations 152 to the inner surface of wall 113. Member 150 serves to cause hot gases of combustion to converge upwardly toward and to pass through opening 146 and then upwardly and about the outer surface of rock box 136. Apex end 140 of the rock box is eccentric to opening 146 (FIG. 5), the latter appearing somewhat oval-shaped because it is truncated. Also, apex end 140 is closer to member 150 at a location 151 adjacent to the open, innermost end 154 of an inclined flue pipe 156 which extends through side wall 113 and into and through conduit 118.

The reason for the eccentricity of end 140 with respect to opening 146 is to assure that a major portion of the combustion gases passing through this opening will contact outer surface 138 of member 137 before entering and being exhausted through flue pipe 156. Thus, there is a minimum of spacing at location 151 between the apex end 140 of the rock box and the adjacent part of member 150, to permit minimum flow of gases therethrough. The larger opening at a location 153 diametrically opposed to location 151 allows a greater volume of the combustion gases to pass upwardly to outer surface 138. It has been found that the combustion gases tend to follow a spiral path as they rise along the outer surface of the rock box. This causes a more efficient heat transfer from the gases to member 137. Since there are no sharp corners on the inner surface of the rock box, the rocks in the rock box can more effectively be heated because they can more effectively contact the inner surface of the rock box.

The second embodiment, as shown in FIGS. 4 and 5, has the preheating capability of the first embodiment. Thus, incoming air is preheated as it passes through conduit 18 and into and through passage 1 16. FIGS. 4 and 5 also show that rock heater 1 10 is mounted on one side of a wall 120 such as the wall of a sauna room. Thus, air from the region exteriorly of the room can be drawn into conduit 118 and preheated as it moves through passage 116.

While the foregoing description has been made with respect to a gas heat source for the rock heaters, it is possible to utilize the teachings of the invention with an electric heater, if desired. The combustion regions mentioned above with respect to rock heaters 10 and would be the source of heated air near an electric heater placed somewhere near or in such region.

The rock heater of this invention is suitable for use with a portable sauna 200 (FIG. 6) which is easy to assemble and is constructed to prevent heat loss from its interior. The sauna is constructed from a number of walls quickly and easily coupled together in a manner to form a sealed housing capable of trapping air within the sauna. To this end, the sauna utilizes improved tongue and groove structure on adjacent walls which permit assembly of the entire unit in a minimum of time, yet allows for building-block assembly so that saunas of different sizes can be erected.

Sauna 200 includes a top wall 202, a front wall 204, a back wall 206 (FIG. 7), a pair of sidewalls 208 and a bottom wall 210. For purposes of illustration, all of the walls are four-sided although they can be of other shapes, if desired.

Top wall 202 is formed from four side members 212 which define a frame secured to the lower surface of a panel 214 of plywood or other material. Each member 212 is milled to present an elongated rib 216 which extends throughout the length of the corresponding member 212. A number of strips 218 of a suitable wood or other material, such as Douglas fir or the like, are secured to members 212 and define the inner surface of top wall 202. Strips 218 are spaced from panel 214 to form a space 220 in which a layer 222 of insulation material, such as fiber-glass, is placed. A metal foil 224 between strips 218 and the insulation material further insulates wall 202. Ribs 216 of the various members 212 of top wall 202 form a generally continuous projection throughout the periphery of top wall 202, such projection being spaced slightly inwardly from the outermost periphery of the top wall (FIG. 8).

Bottom wall 210 is formed from four side members 226 (FIG. 8) which are identical to members 212. Each member 226 has a rib 228 which is vertically aligned with a corresponding rib 216 thereabove. Bottom wall 210 further includes a bottom panel 230 coupled to side members 226 and cross strips 232 for supporting panel 230 above a floor.

Sidewalls 208 are substantially identical in construction and, for purposes of illustration, each sidewall has two identical sections 244 and 246 (FIG. 7). Each sidewall section has four side members 236 connected to the inner surface of an outer panel 238 of plywood or the like. Strips 240, similar to strips 218, are also attached to members 236, strips 240 defining the inner surface of the corresponding sidewall section.

Each side member 236 has a centrally disposed, outer peripheral groove 242 therein for receiving a rib on an adjacent wall. For instance, FIG. 8 shows how a rib 216 of top wall 202 is received within the adjacent groove 242 to interconnect the sidewall section and the top wall.

Each side member 212 is milled or otherwise shaped to not only form the corresponding rib 216 but also to form a recess 217 for receiving a portion of the adjacent sidewall as shown in FIG. 8. This feature assures a tight seal for the junction of the two walls to thereby serve as a trap for keeping hot, moist air within the sauna.

Each sidewall section has a space between panel 238 and strips 240 for receiving a layer 250 of insulation material. A metal foil 252 is adjacent to the outer surfaces of strips 240. Also, the adjacent sidewall sections 244 and 246 are coupled together by a vertical strip 248 (FIG. 7) received within the adjacent grooves 242 of abutting side members 236.

Front wall 204 has a pair of vertical side members 254 (only one of which is shown in FIG. 7), each member 254 having a rib 256 for insertion into the adjacent groove 242. Each member 254 also has a recess 258 (FIG. 7) for receiving a portion of the adjacent sidewall section. Thus, a tight seal of the type mentioned above is formed when the front wall becomes coupled to the adjacent sidewall sections. Also, the front wall has spaced upper and lower side members (not shown) which are identical to side members 236 of the sidewall sections to present upper and lower grooves for the front wall.

The front wall also has an outer panel 260, inner strips 262 similar to and for the same purpose as strips 218 and 240 and a layer of insulating material and a metal foil sheet in the space between panel 260 and 262. The front wall can also be made in sections as described above with respect to the sidewalls by using a side member 264 (FIG. 7) identical to side members 236 of the sidewallsections and a strip 266 for coupling side member 264 to the corresponding side member of the adjacent front wall section.

Rear wall 206 is substantially the same in construction as the front wall except that the latter has a door assembly 234 formed therein. Such door assembly has means for mounting the same on the front wall in a manner such that hot, moist air will be trapped in the sauna.

In use, the vertical walls of the sauna are coupled to bottom wall 210 by placing the lower groove or grooves of each vertical wall over the adjacent rib 228 of the bottom wall and then lowering the vertical wall onto the bottom wall. When the vertical walls are in place, the top wall is moved onto the vertical walls and lowered slightly until ribs 216 are seated in the adjacent upper grooves of the vertical walls. Thus, the assembly of the sauna is complete, thereby permitting the installation of the rock heater in the sauna.

The tongue and groove structure described above allows the walls of the sauna to be of any desired dimensions. Thus, sidewalls 208 could be longer or shorter in length as could be the front and rear walls providing the top and bottom walls are sized commensurately. To allow for this, walls made in stock sizes could be made and be available to fill the needs for saunas of different sizes. Generally, the sauna will be made completely of wood and various grades and types of wood can be used to form the walls.

Sauna 200 can be readily disassembled and stored or moved to a different location. The above assembly steps are reversed to disassemble the sauna.

FIG. 9 and 10, similar to FIGS. 7 and 8, illustrate another embodiment of the sauna having walls whose ribs and grooves are reverse of those of the embodiment of FIGS. 7 and 8. For instance, a sidewall 270 has four outer peripheral side members 272 provided with ribs 274 centrally disposed thereon. These ribs are received within corresponding grooves of the front wall member 276 and the back wall member (not shown). A number of vertical posts 270 can be used to form the front and rear walls with the grooves in the posts being arranged to form the junctions between the sidewalls and the front and rear walls. Also, posts 270 can be used to interconnect a pair of adjacent sidewall sections as shown in FIG. 9, the latter also showing a door assembly 278 coupled to the front wall. The walls of the second embodiment are insulated in the same manner as those of the first embodiment.

I claim:

1. A rock heater for a sauna bath comprising: a generally continuous sidewall; a rock box closing the top of the sidewall and extending into the region surrounded thereby, the lower portion of the sidewall defining a space in which hot gases can be generated and from which such gases can rise and contact the outer surface of the rock box; means at least partially surrounding the sidewall for defining a fluid passage extending along and in heat transfer relationship to the outer surface of the sidewall, said passage being in fluid communication with said space whereby air to support the heating of gases can be directed thereinto; an exhaust conduit adjacent to the outer surface of the rock box for directing exhaust gases outwardly of said sidewall; and means adjacent to said exhaust conduit for directing air into said passage.

2. A rock heater as set forth in claim 1, wherein said rock box has a polygonal outer surface.

3. A rock heater as set forth in claim 2, wherein said exhaust conduit extends through the bottom of the rock box and is adapted to be placed in heat transfer relationship to the rocks in said rock box.

4. A rock heater as set forth in claim 1, wherein said rock box has a conical outer surface and a closed apex end at its lower extremity.

5. A rock heater as set forth in claim 4, wherein is provided a conical member having a central opening therein and having its apex near its uppermost extremity, the apex end of the rock box being adjacent to said opening, the latter defining a fluid passage for the upward flow of combustion gases from said combustion region whereby said gases can move into heat transfer relationship with the outer surface of said rock box.

6. A rock heater as set forth in claim 5, wherein the opening in said conical member is eccentric with respect to the apex end of said rock box.

7. A rock heater as set forth in claim 5, wherein the apex end of the rock box is closer to the conical memher at one side of the latter than to the opposite side thereof.

8. A heater for use in a sauna bath comprising: a wall for dividing a space into two regions; a furnace in the region on one side of the wall and having a burner apparatus for producing hot gases of combustion when an air-gas mixture is supplied to the burner apparatus and ignited; a casing surrounding the furnace, at least a portion of the casing being spaced from the furnace to present an air flow passage therebetween, a major portion of the passage being in heat exchange relationship with the furnace and disposed in fluid communication with the burner apparatus to supply the air for the airgas mixture; conduit means extending through said wall and coupled with the passage for connecting the latter with a region on the opposite side of the wall, whereby air can flow from the last-mentioned region and through said passage; and a rock box coupled to the furnace and disposed in the path of the hot gases of combustion produced thereby, whereby rocks in the rock box will be heated to the desired temperature.

9. A rock heater for use in a sauna bath comprising: a wall dividing a space into two regions; a furnace in the region on one side of the wall; a casing surrounding the furnace, at least a portion of the casing between spaced from the furnace to present an air flow passage having a major portion extending along said furnace and in heat exchange relationship thereto; burner apparatus within the furnace and having a portion within the fluid passage, said burner apparatus adapted to be coupled to a source of gas and having a first opening communicating with said fluid passage whereby air can combine with the gas to provide an air-gas mixture; conduit means extending through said wall for coupling the fluid passage with the region on the opposite side of the wall, whereby air in the last-mentioned region can be drawn into the passage for providing the air for said airgas mixture, there being a second opening connecting the fluid passage with the interior of the furnace to allow air to enter the latter and support combustion adjacent to the burner apparatus; a rock box carried by the furnace and disposed in the path of the hot gases of combustion produced by the burner apparatus, whereby rocks in the rock box will be heated when the gases rise and contact the rock box; and exhaust means adjacent to the rock box for exhausting the bases of combustion to an area remote from the furnace.

10. A heater as set forth in claim 9, wherein said first opening is adjacent to the bottom of the furnace and said conduit means is adjacent to the top of the furnace.

l l. A heater as set forth in claim 9, wherein said casing has a side wall which is spaced from a side wall of the furnace to present a side passage, the bottom of the casing being spaced from the bottom of the furnace to present a bottom space communicating with the side passage, said conduit means being disposed adjacent to the upper end of the casing, whereby air flowing into the conduit means will pass downwardly along the side of the furnace and be preheated thereby.

112. A heater as set forth in claim 9, wherein said rock box extends into the top of the furnace and closes the same, said exhaust means extending laterally from said rock box.

13. A heater as set forth in claim 9, wherein said rock box has inclined side walls to present a space exteriorly of the side walls and within said furnace for receiving the hot gases of combustion from the burner apparatus, said exhaust means extending through and laterally of said rock box.

M. In a rock heater: a substantially continuous side wall having an upper open end and defining a combustion region therewithin; a rock box extending into and closing the upper end of said side wall, said rock box having a conical outer surface and a closed apex at its lowermost extremity; means within said side wall for funnelling combustion gases toward and into heat transfer relationship with said apex, whereby said gases will move upwardly from said apex and into heat transfer relationship to said conical outer surface; and means adjacent to the rock box for exhausting said gases from within said side wall.

15. In a rock heater as set forth in claim M, wherein said funnelling means includes a conical member having an open apex at its upper extremity, said member being secured at its outermost periphery to said side wall, the apex of said rock box being adjacent to the apex of said conical member.

16. In a rock box as set forth in claim 15, wherein the apex of the rock box extends partially into the opening of the apex of said conical member.

17. In a rock box as set forth in claim 14, wherein said funnelling means includes a conical member having its apex at its upper extremity, there being an opening through the last-mentioned apex, the lower outer periphery of the conical member being secured to the inner surface of the side wall, the apex of said rock box being adjacent to the opening in the apex of said conical member.

18.. In a rock box as set forth in claim 17, wherein said exhausting means includes an exhaust conduit having an open end in fluid communication with the region surrounding the apex of said rock box.

19. In a rock box as set forth in claim 18, wherein is provided an air entrance conduit surrounding said exhaust conduit and in fluid communication with said combustion region.

20. In a rock box as set forth in claim 19, wherein is provided means in heat transfer relationship to said side wall for placing said air entrance conduit in fluid communication with said combustion region.

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